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这时可用typeof()来判断变量是string 还是number来区分0和“”，
typeof(undefined) == ‘undefined‘ typeof(null) == ‘object‘ typeof("") == ‘string‘ typeof(0) == ‘number‘ typeof(false) == ‘boolean‘
JavaScript判断变量类型
原文地址：http://www.cnblogs.com/xbblogs/p/5329914.html
typeof(null) == ‘object‘ typeof("") == ‘string‘ typeof(0) == ‘number‘ typeof(false) == ‘boolean‘